Chemical reactor

ABSTRACT

A chemical reactor is disclosed and which has a core composed of a stack of metal plates that are diffusion bonded in face-to-face relationship. A plurality of reaction zones are located within the core, as are a plurality of catalyst receiving zones, and both the reaction zones and the catalyst receiving zones are defined by respective aligned apertures in the plates. A first channel arrangement is provided in some of the plates for transporting a first reactant to and between the reaction zones, portions of the first channel arrangement that interconnect the reaction zones being formed over at least a portion of their length as heat exchange channels. A second channel arrangement is provided in others of the plates and is arranged to deliver a second reactant to each of the reaction zones. Also, a third channel arrangement provided in still others of the plates for transporting a third reactant to and between the catalyst receiving zones, portions of the third channel arrangement that interconnect the catalyst receiving zones being formed over at least a portion of their length as heat exchange channels that are positioned in heat exchange proximity to the heat exchange channels of the first channel arrangement. Also disclosed is a fuel processor that incorporates the chemical reactor, the catalyst receiving zones being arranged to function as reformer stages in the fuel processor.

FIELD OF THE INVENTION

This invention in broad terms relates to an apparatus for use in, and amethod of, effecting a chemical reaction. The invention has beendeveloped in relation to a steam methane reformer for use in associationwith a proton exchange membrane fuel cell and the invention is hereindescribed in that context. However it will be understood that both theapparatus and the method of the invention do have broader applications,to other reactive processes.

BACKGROUND OF THE INVENTION

Reforming processes are conventionally effected in tubular reformers,with catalyst packed into a plurality of reactor tubes. Heat is applieddirectly to and transferred through the walls of the tubes in a mannerto maintain radial and axial temperature profiles inside the tubeswithin required limits, and this approach has been more-or-lesssuccessful. However, it does require the establishment of a fine balancebetween reaction and heat transfer within the tubes, heat transfer tothe outside of the tubes and pressure drop.

The establishment of this balance and the consequential need forrelatively large catalyst particles result in low catalyst effectivenessand the need for reformers that are inherently bulky. The catalysteffectiveness might be enhanced and the size of the reformers might bereduced if smaller catalyst particles having higher activity were to beused, but pressure-drop constraints would then dictate the use of many,parallel, short tubes in the reformers.

Some consideration has been given to the possible development of analternative to the tubular reformers; that is, to the use of so-calledprinted circuit heat exchanger (“PCHE”) cores and to the deposition ofthin layers of reforming catalyst into channels of plates that form thecores. The PCHE cores currently are used in heat exchangers, and theyare constructed by etching channels having required forms and profilesinto one surface of individual plates which are then stacked anddiffusion bonded to form cores having dimensions required for specificapplications.

However, whilst this alternative (projected) approach does indicate somemerit, several problems are foreseen, including the following:

-   -   Difficulties in obtaining adhesion of catalyst to the metal        (plate) substrate,    -   Limited catalyst life,    -   Difficulties in replacing the catalyst, and    -   Coupling of heat transfer and catalyst areas, this requiring        very high-activity catalyst if over-investment in heat exchange        surface is to be avoided.

A partial solution to these problems is revealed in United States PatentPublication US2002/0018739 A1, dated 14 Feb. 2002, which (withoutconstituting common general knowledge) discloses a chemical reactorhaving a PCHE-type core. The core is constructed with alternating heatexchange and catalyst-containing zones that together form a passagewayfor a reactant. Each of the heat exchange zones is formed from stackeddiffusion bonded plates, with some of the plates providing channels for(externally heated or cooled) heat exchange fluid and others of theplates providing orthogonally directed channels to carry the reactantfrom one catalyst-containing zone to the next such zone.

The present invention in one of its applications is directed to adevelopment which alleviates at least some of the problems of tubularreformers and which facilitates or extends, in a novel way, the use ofPCHE cores in chemical reactors.

SUMMARY OF THE INVENTION

The present invention may be defined broadly as providing a chemicalreactor comprising:

-   -   a) a core composed of at least one stack of metal plates bonded        in face-to-face relationship,    -   b) a plurality of reaction zones located within the core,    -   c) a plurality of catalyst receiving zones located within the        core,    -   d) a first channel arrangement provided in at least some of the        plates for transporting a first reactant to and between the        reaction zones, portions of the first channel arrangement that        interconnect the reaction zones being formed over at least a        portion of their length as heat exchange channels,    -   e) a second channel arrangement provided in at least some of the        plates and arranged to deliver a second reactant to each of the        reaction zones, and    -   f) a third channel arrangement provided in at least some of the        plates for transporting a third reactant to and between the        catalyst receiving zones, portions of the third channel        arrangement that interconnect the catalyst receiving zones being        formed over at least a portion of their length as heat exchange        channels that are positioned in heat exchange proximity to the        heat exchange channels of the first channel arrangement.

The invention may also be defined in broad terms as providing a methodof effecting a chemical reaction by:

-   -   directing a first reactant into and serially through the        reaction zones in the above defined reactor by way of the first        channel arrangement,    -   directing a second reactant in parallel feeds into the reaction        zones by way of the second channel arrangement, the second        reactant being selected to react exothermically with the first        reactant in the respective reaction zones, and    -   concurrently directing a third reactant into and serially        through a catalyst contained in the catalyst receiving zones by        way of the third channel arrangement and, in so doing, exposing        the reactant to heat from the product of the exothermic reaction        in its passage through the heat exchange channels of the first        channel arrangement.

Depending upon the process, the reaction zones may also be charged witha catalyst that is selected to provide for catalytic reaction (eg,combustion) of the first and second reactants.

OPTIONAL FEATURES OF THE INVENTION

The core of the above defined reactor may be constructed from pluralstacks of the metal plates and, in such a case, the adjacent stacks maybe spaced apart by interconnecting walls that define the reaction zonesand the catalyst receiving zones. Such an arrangement is considered tobe especially suitable for large capacity reactors.

However, for at least some reactors, the core may comprise a singlestack of metal plates. In this case each of the reaction zones will bedefined by aligned apertures in adjacent ones of the plates and each ofthe catalyst receiving zones will similarly be defined by (further)aligned apertures in adjacent ones of the plates.

The number of reaction zones within the core may be the same as ordifferent from the number of catalyst receiving zones. In a specificembodiment of the invention the reaction zones are arrayed in twoparallel rows, with the first channel arrangement extending linearlybetween the reaction zones. Also, in this case, the catalyst receivingzones may be arrayed in three parallel rows, one of which is locatedbetween of the rows of reaction zones and the other two of which arelocated outside of the rows of reaction zones.

For some applications of the invention the metal plates may be stackedin repeating groups of three superimposed plates, with one of the threeplates being formed with the first channel arrangement for transportingthe first reactant to and between the reaction zones, a second of thethree plates being formed with the second channel arrangement fordelivering the second reactant to the reaction zones and the third plateof each group being formed with the third channel arrangement fortransporting the third reactant through the catalyst receiving zones.

In order to optimise heat transfer between the product of the exothermicreaction and the third reactant, the first and third plates may bediffusion bonded in face-to-face contacting relationship.

In other applications of the invention, for example when the reactorembodies or is constructed as a reformer, it may be necessary ordesirable to exchange heat between portions of the (same) reactantstream that are at different processing stages. Also, it may bedesirable in some cases to allocate a single processing function to twoor more plates and/or to increase the number of plates for the purposeof optimising heat exchange. In such cases it will be necessary to stackthe plates in repeating groups of four or more plates. The order inwhich the plates of each group will be interleaved and diffusion bondedwill be dependent upon the requirements of specific processes andchannel formats embodied in the plates.

Embodiments of the invention have applications in any process thatrequires catalytic conversion of a reactant and heating of the reactantbetween catalytic reaction stages. However, in a specific embodiment ofthe invention the reactor comprises or incorporates a reformer such as asteam methane reformer for use in association with a proton exchangemembrane fuel cell or other application requiring hydrogen or syngas. Insuch case the reactor may be incorporated in a fuel processor that mayinclude at least one pre-reformer that is arranged to be heated by hotsyngas, at least one pre-reformer that is arranged to be heated by hotflue gas and, as portions of the reactor, multiple reformers arranged tobe heated indirectly by catalytic combustion of, for example, anodeoff-gas. In this arrangement the first reactant may comprise acombustion supporting gas and the second reactant may comprise acombustible gas such as anode off-gas.

The fuel processor, of which the reactor may be a part, may alsoincorporate ancillary processing stages, including cooling andpre-heating stages, water-gas shifting and CO oxidation. Some or all ofthese stages may be incorporated in a further core (or further cores)that is (or are) similar to the reactor core, the further core(s) havingappropriate channel arrangements in stacked metal plates.

The invention will be more fully understood from the followingdescription of a specific embodiment of a reactor in the form of a steammethane reformer that is incorporated in a fuel processor. Thedescription is provided with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a diagrammatic representation of the fuel processorconnected to an associated proton exchange membrane fuel cell (“PEMFC”),

FIG. 2 shows a diagrammatic representation of the fuel processor shownin FIG. 1, including a reactor having reforming and pre-reformingstages,

FIG. 3 shows a temperature profile of the pre-reforming stages,

FIG. 4 shows a temperature profile of the reforming stages,

FIG. 5 shows a temperature profile of the combined pre-reforming andreforming stages,

FIG. 6 shows a graph of syngas heat recovery,

FIG. 7 shows a graph of flue heat recovery,

FIG. 8 shows a perspective view of the core of the fuel processor inisolation from associated fluid supply and discharge pipework, and

FIG. 9 shows, in superpositioned relationship, a group of six metalplates that are stacked and diffusion bonded with further such groups toform the core.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

As shown in FIGS. 1 and 2, the fuel processor 10 is in use connected toa PEMFC 11, and pipework indicated by the arrowed connections isprovided to deliver the various indicated fluids (this term embracingboth liquids and gases in this specification) to and from the fuelprocessor. The fuel processor 10 is shown in block-diagrammatic form inFIG. 2 but, as will be described later, portions of the fuel processorare embodied in a single core that is composed of diffusion bondedplates.

The fuel processor 10 may be considered as including seven notionallyseparate portions or modules 12 to 18 that provide the followingfunctionality:

-   -   12—Anode gas cooling.        -   Methane/Water pre-heating.    -   13—Syngas cooling/CO oxidation/Water Gas Shift (WGS).        -   Water boiling.    -   14—Syngas cooling.        -   Methane (“feed gas”) pre-heat/pre-reforming.    -   15—Flue gas cooling.        -   Anode off-gas (“fuel”)/Air pre-heat.    -   16—Flue gas cooling.        -   Water boiling.    -   17—Flue gas cooling.        -   Feed pre-heat/pre-reforming.    -   18—Multi-stage combustion.        -   Multi-stage heating of reactant.        -   Multi-stage reforming.

Significant ones of these functions will be described in more detaillater in this specification.

The feed gas is, as shown, subject to stepwise reforming involving:

-   -   Three pre-reformers 19 heated by hot syngas in portion 14,    -   Two pre-reformers 20 heated by hot flue gas in portion 17, and    -   Nine reformers 21, in reactor portion18, that are heated        indirectly by catalytic combustion of the anode off-gas.

The temperature profiles for the pre-reforming and reforming stages19/20 and 21 are shown in FIGS. 3 and 4 respectively and the compositetemperature profile is shown in FIG. 5. As indicated, the maximumreforming temperature is held below 800 degrees C. because highertemperatures are not essential at intended low operating pressures. Anymethane slip will constitute an “inert” at the fuel cell anode andultimately will usefully be burned in the combustors.

In the relatively low temperature pre-reforming stages higherhydrocarbons are converted and the hydrogen content is increased wellbelow methane cracking temperatures. Above 650 degrees C. carbonformation from methane cracking occurs more quickly than the carbonremoval reactions if the methane cracking equilibrium is unfavourable,so high hydrogen levels are required by the time this temperature isreached. The six stages of pre-reforming and reforming that are shown tooccur below 650 degrees C. help to ensure that that carbon activityremains below unity at temperatures above 650 degrees.

Also, the fuel processor as shown in FIG. 2 integrates features thatfacilitate passive control (ie, self regulation) of operation.

The heat exchangers may be sized and configured such that thetemperature profile shown in FIG. 5 is substantially maintained evenunder conditions of substantial turn-down. Only the maximum reformertemperature requires independent control, by controlling the fuel supplyrate.

Counter-flow and co-flow heat exchangers are employed. Both pinch up asflow rates fall, without substantially affecting boundary temperatures.

The split, parallel feed of fuel to the catalytic combustors, the airsupply to the two stages of selective CO oxidation and the water supplyto the heat exchangers are all integrated into the fuel processor.

Water may be supplied at the rate required to maintain the liquid levelin the phase separator, from which provision may be made for a netoutflow of steam and a small liquid blow-down. The steam ratio remainsreasonably constant with capacity as the availability of heat to raisesteam varies with the methane throughput.

Reference is now made to FIGS. 2 to 7 and to the functionality of thevarious portions 12 to 18 of the fuel processor.

In portion 12 a three-stream, counter-flow heat exchanger 22 is employedto preheat the water and methane in the final cooling stage of thesyngas, and an internal pinch occurs at the point where watercondensation begins on the syngas side. The three-stream heat exchangerpermits relatively high effectiveness to be achieved, as shown in FIG.6, and avoids the need for a controlled split of the syngas stream topreheat the methane and water streams in separate exchangers.

In relation to portion 13, as shown in FIG. 2, it is observed that COlevels should typically be held below 10 ppm for a PEMFC. This requiresa selective oxidation (COOX) reaction following the water gas shift.Both of the reactions, as shown, occur in two stages in portion 13.

The heat load for steam raising is relatively high, being abouttwo-thirds of that required from combustion in the reformer stage. Muchof the heat recovery from the hot process streams is therefore committedto water boiling, and both the exothermic WGS and COOX reactions can runabove the water boiling point, contributing to the steam raising. Asindicated water is boiled in a thermosyphon loop in the heat exchangersfollowing these reactions and this provides an opportunity forblow-down, minimising the quality requirements for make-up water, andavoids dryout on the heat exchange surfaces with high vapour quality.

In portion 15, above the water boiling point, the heat from the hotsyngas is used to pre-heat the feed stream. Sufficient heat can be madeavailable to drive the three illustrated stages of preheat, which isfavourable for the reasons that:

-   -   C2+ molecules in the feed are converted to methane at low        temperatures, without risk of coking,    -   Hydrogen levels are increased at low temperature, without risk        of methane cracking and, as indicated, the high grade heat is        used for the purpose of pre-reforming in the three pre-reformer        stages 19.

Two heat exchangers 24 provide counter-flow exchange and the third heatexchanger 25 provides co-flow exchange, in order to lock-in a requiredtemperature profile during turndown. The co-flow in the third exchangeris provided to counter the possible danger of overheating the feedstream and cracking methane.

In portion 15 a three-stream heat exchanger 26 is again employed, withthe fuel and air being preheated separately to avoid the need for acontrolled split of the flue gas. The preheated air is passed seriallythrough the illustrated nine stages of catalytic combustion in portion18, whilst the preheated fuel is fed to combustion zones 27 in parallelstreams in order to limit the temperature rise in each zone.

Most of the steam for the processor is raised in the heat exchanger 23in portion 16, the heat exchanger operating as a once-through boilerwhich provides an exit quality below about 70% which avoids thepossibility of dry-out.

The two further stages 20 of pre-reforming are provided in portion 17for the purpose of generating relatively low temperature hydrogen,further protecting against methane cracking in the reformer stages 21 inportion 18. One associated heat exchanger 28 is arranged to providecounter-flow exchange and the other heat exchanger 29 provides forco-flow exchange, in order to lock-in a required temperature profileduring turndown, without risk of overheating the feed.

FIGS. 6 and 7 of the drawings are relevant to the preceding descriptionof the processor portions 13 to 17 in that they show graphically thetemperature profiles of the syngas and flue gas heat recoveryrespectively.

The reformer itself, in portion 18 of the fuel processor consists of thenine stages 21 of reforming reaction which are driven by the nine stages27 of anode off-gas combustion. The reactions on both sides occur inessentially adiabatic beds, with heat exchangers 30 providing heatexchange between the fluids as they pass between the respectiveadiabatic beds.

Fluid circuitry within the reformer portion provides for splitting ofthe anode off-gas into nine parallel streams, as indicated in FIG. 2,and, as will be apparent from plate configurations to be referred tobelow, further sub-division of the fuel in those streams into numerousparallel streams for intimate mixing into the combustion supporting airprior to combustion at each stage 27.

The ascending temperature profile for the reformer, as shown in FIG. 5,is driven by this circuitry without further active control. As indicatedpreviously, only the maximum reformer temperature requires continuouscontrol through the total fuel supply rate.

Portions 17 and 18 of the fuel processor as shown diagrammatically inFIG. 2 may be embodied in the core 31 which is shown, also somewhatdiagrammatically, in FIG. 8. Associated fluid supply and dischargepipework (as indicated schematically in FIG. 1) are omitted from FIG. 8and primary features only of the core are illustrated. The features thatare omitted, for descriptive convenience, will be understood and readilyascertainable by persons who are familiar with contextual technology.

The core 31 comprises a single stack of diffusion bonded plates 32, thetotal number of which will be dependent upon the capacity required ofthe fuel processor in any given application, and the core incorporatestwo parallel rows of nine reaction zones 33 which, in the case of theabove described fuel processor, comprise the combustion zones 27.

The reaction zones 27/33 are fed with a first reactant (ie, thecombustion supporting gas in the case of the fuel processor) by way ofend ports (not shown) in the core. Also, the reaction zones 27/33 arefed with a second reactant (ie, fuel in the case of the fuel processor)by way of inlet ports 34.

The core 31 further incorporates three parallel rows of nine catalystreceiving zones 35 and 35A which, in the case of the fuel processor,comprise the above mentioned pre-reforming and reforming regions 20 and21 of portions 17 and 18 of the fuel processor. The catalyst receivingzones are fed with a third reactant (ie, the methane and steam in thecase of the fuel processor) by way of inlet and outlet ports in the topand/or bottom of the core as viewed in FIG. 8.

The plates 32 are all formed with generally rectangular apertures,various ones of which align to form the reaction zones 33 and thecatalyst receiving zones 35. The plates are stacked in repeating groupsof six plates, one of which groups is shown in FIG. 9 and comprises,from the top down:

-   -   Plate 32A—which carries the first reactant (ie, the combustion        supporting gas).    -   Plate 32B—which carries the second reactant (ie, the fuel).    -   Plate 32C(1)—which carries a first stream of the third reactant        (ie, syngas 1).    -   Plate 32A—which carries the first reactant (ie, the combustion        supporting gas).    -   Plate 32B—which carries the second reactant (ie, the fuel).    -   Plate 32C(2)—which carries a second stream of the third reactant        (ie, syngas 2).

All of the plates are formed from a heat resisting alloy such asstainless steel and all plates typically have the dimensions 600 mm by100 mm. The plates 32A, C(1) and C(2) have a thickness of 1.6 mm and theplates 32B have a thickness of 0.7 mm.

A first channel arrangement 36 is provided in the plates 32A fortransporting the first reactant to and between the apertures 33 thatdefine the reaction zones 27. The channel arrangement extends linearlybetween supply and discharge ports that, in use of the processor, arelocated at the ends of the core 31. Portions 37 of the channelarrangement that extend between and, in some cases beyond, adjacentpairs of the apertures 33 function, in use, as heat exchange channels.

A second channel arrangement 38 is provided in the plates 32B fordelivering the second reactant in parallel streams to each of thereaction zones 33 from the supply ports 34. The second channelarrangement incorporates a large number of feed branches thatcommunicate with the reaction zones 33 to facilitate intimate mixing ofthe first and second reactants (ie, the air and combustible gas in thecase of a fuel processor) in the reaction zones 33.

A third channel arrangement 39 is provided in each of the plates 32C(1)and 32C(2) for transporting the third reactant in parallel streams toand between the catalyst receiving zones 35 and 35A in the respectiveplates. Serpentine shaped portions 40 of the third channel arrangementare positioned to locate in heat exchange proximity to the heat exchangeportions 37 of the first channel arrangement 36 in the plates 32A withwhich the plates 32C(1) and C(2) have surface contact.

The various channels in the plates 32A and 32C(1) and C(2) aresemi-circular in cross-section and have a radial depth of 1.0 mm, andthose in plates 32B have a radial depth of 0.4 mm.

As previously described, the plates 32 are stacked and diffusion bondedin face-to-face relationship; that is, with the (front) channelled faceof each plate in contact with the (rear) un-channelled face of itsadjacent plate.

Variations and modifications may be made in respect of the fuelprocessor and its component parts as above described without departingfrom the scope of the invention as defined in the appended claims. Forexample, the order of plate stacking, the positioning of the variousreaction zones and the dispositions and configurations of the variouschannel arrangements may be changed extensively from those that havebeen described and illustrated.

1. A chemical reactor comprising: a) a core composed of at least onestack of metal plates bonded in face-to-face relationship, b) aplurality of reaction zones located within the core, c) a plurality ofcatalyst receiving zones located within the core, d) a first channelarrangement provided in at least some of the plates for transporting afirst reactant to and between the reaction zones, portions of the firstchannel arrangement that interconnect the reaction zones being formedover at least a portion of their length as heat exchange channels, e) asecond channel arrangement provided in at least some of the plates andarranged to deliver a second reactant to each of the reaction zones, andf) a third channel arrangement provided in at least some of the platesfor transporting a third reactant to and between the catalyst receivingzones, portions of the third channel arrangement that interconnect thecatalyst receiving zones being formed over at least a portion of theirlength as heat exchange channels that are positioned in heat exchangeproximity to the heat exchange channels of the first channelarrangement.
 2. The chemical reactor as claimed in claim 1 wherein thecore comprises a single stack of metal plates which are diffusion bondedin face-to-face contacting relationship.
 3. The chemical reactor asclaimed in claim 2 wherein each of the reaction zones is defined byaligned apertures in adjacent plates of the stack.
 4. The chemicalreactor as claimed in claim 2 wherein each of the catalyst receivingzones is defined by aligned apertures in adjacent plates of the stack.5. The chemical reactor as claimed in claim 2 wherein the reaction zonesare arranged to constitute combustion zones.
 6. The chemical reactor asclaimed in claim 2 wherein the reaction zones are charged with acatalyst that is selected to provide for catalytic combustion of thefirst and second reactants.
 7. The chemical reactor as claimed in claim2 wherein the plates are stacked in repeating groups of six superimposedplates, with the first and fourth plates (in descending order) beingformed with the first channel arrangement for transporting the firstreactant to and between the reaction zones, the second and fifth platesbeing formed with the second channel arrangement for delivering thesecond reactant to the reaction zones and the third and sixth platesbeing formed with the third channel arrangement for transporting thethird reactant to and between the catalyst receiving zones.
 8. Thechemical reactor as claimed in claim 7 wherein the second and fifthplates have a thickness that is less than that of the other plates ineach group.
 9. The chemical reactor as claimed in claim 7 whereinchannel elements that form the second channel arrangement have across-sectional area that is smaller than that of channel elements thatform the first and third channel arrangements.
 10. The chemical reactoras claimed in claim 1 wherein the reaction zones are arrayed in twoparallel rows and the first channel arrangement extends linearly betweenthe reaction zones.
 11. The chemical reactor as claimed in claim 10wherein the catalyst receiving zones are arrayed in three parallel rows,one of which is located between the rows of reaction zones and the othertwo of which are located outside of the rows of reaction zones.
 12. Thechemical reactor as claimed in claim 1 when in the form of a reformerthat is suitable for use in association with a fuel cell.
 13. Thechemical reactor as claimed in claim 2 when embodied in a fuel processorhaving a reformer stage that incorporates the reaction zones, when inthe form of conduction zones, and the catalyst receiving zones.
 14. Thechemical reactor as claimed in claim 2 when embodied in a fuel processorfor use in association with a proton exchange membrane fuel cell, thefuel processor having a reformer stage that incorporates the reactionzones, when in the form of conduction zones, and the catalyst receivingzones.
 15. The chemical reactor as claimed in claim 13 wherein the fuelprocessor, of which the reactor forms a part, incorporates at least onepre-reformer stage incorporating at least one of the catalyst receivingzones.
 16. The chemical reactor as claimed in claim 15 wherein the fuelprocessor incorporates at least one pre-reformer that is arranged to beheated by a hot syngas.
 17. The chemical reactor as claimed in claim 15wherein the fuel processor incorporates at least one pre-reformer thatis arranged to be heated by hot flue gas that is, in use, directedthrough a portion of the third channel arrangement.
 18. A method ofeffecting a chemical reaction in a chemical reactor as claimed in anyone of the preceding claims and which comprises the steps of: directinga first reactant into and serially through the reaction zones in thechemical reactor by way of the first channel arrangement, directing asecond reactant in parallel feeds into the reaction zones by way of thesecond channel arrangement, the second reactant being selected to reactexothermically with the first reactant in the respective reaction zones,and concurrently directing a third reactant into and serially through acatalyst contained in the catalyst receiving zones by way of the thirdchannel arrangement and, in so doing, exposing the reactant to heat fromthe product of the exothermic reaction in its passage through the heatexchange channels of the first channel arrangement.